The present invention relates generally to combine harvesters and, more particularly, to a rotary cleaning mechanism in combines for cleaning unwanted residue, such as chaff, straw, etc., from threshed grain.
Conventional cleaning systems clean threshed grain by blowing air through a set of planar sieves utilizing gravitational forces to urge cleaned grain through the sieve openings. With the advent of higher capacity threshing and separating mechanisms, such as rotary axial flow combines, the capacity for threshing grain has increased beyond the capacity of conventional cleaning systems to clean the grain. Accordingly, it is desirable to increase both the capacity and the efficiency of cleaning systems in combine harvesters so as not to limit the throughput capability of the combine.
In rotary cleaning devices utilizing centrifugal force generated by the rotation of the cleaning cylinder to urge clean grain through the sieve openings, it is important to get the threshed grain outwardly onto the cleaning cylinder in a positive manner so that the centrifugal forces can act on the threshed grain to effect a cleaning action thereon. Directly discharging the threshed grain from a centrally located distributing device onto cleaning sieves can cause the sieves to plug, thereby destroying the cleaning action in this portion of the cleaning cylinder. Furthermore, to assure maximum capacity of the rotary cleaning cylinder, it is important to provide an infeed mechanism that will aggressively convey threshed grain into the cleaning cylinder without plugging or clogging.